The Data Over Cable Service Interface Specifications (DOCSIS for short) is an international standard developed by a cable standardization organization (Cable Labs). The DOCSIS 3.0 Physical Layer (PHY for short) Specification defines that when a cable modem (CM for short) transmitter sends an upstream signal to a cable modem termination system (CMTS for short) receiver, pre-equalization processing needs to be performed to cancel interference (including a group delay and a micro-reflection) and increase a modulation error ratio (MER for short) of a constellation of a signal received by a CMTS.
In the DOCSIS 3.0 PHY Specification, an adaptive pre-equalization solution used when a CM sends an upstream signal is shown in FIG. 1. The CM includes a square root raised cosine (SRRC for short) filter and a pre-equalizer unit. The pre-equalizer unit uses a transversal filter structure shown in FIG. 1. The CMTS includes an SRRC filter and an adaptive equalizer unit. The adaptive equalizer unit in the CMTS obtains 24 equalizer coefficients (Wn, where n=1, 2, . . . , 24) after performing initial ranging calculation and periodic ranging calculation according to a received known preamble sequence, and then transmits the 24 equalizer coefficients as 24 pre-equalizer coefficients (Fn=Wn, where n=1, 2, . . . , 24) of the pre-equalizer unit to the CM by using a ranging response (RNG-RSP for short) message, so that the coefficients are used to perform pre-equalization on a signal.
To cancel interference, the prior art uses the solution shown in FIG. 1 in which the adaptive equalizer unit of the CMTS calculates 24 equalizer coefficients by using a preamble sequence and transmits the coefficients as 24 pre-equalizer coefficients of the pre-equalizer unit to the CM by using an RNG-RSP message, and then the CM uses the received 24 pre-equalizer coefficients to perform pre-equalization on a signal. In the solution, a main tap location of the 24 pre-equalizer coefficients of the CM is set to 8, so that 8 pre-equalizer coefficients are used to cancel an impact of a group delay, and that remaining 16 pre-equalizer coefficients are used to cancel an impact of micro-reflection. In addition, the adaptive equalizer unit of the CMTS generally calculates the 24 equalizer coefficients by using a fixed step size nested in multiple iterations while using an adaptive algorithm.
The solution in the prior art has the following problem: Because accuracy of the equalizer coefficients obtained by the CMTS through calculation is not sufficiently high, performance of interference cancellation is poor.